I often carry fast food for short backpacking trips (usuallly 2-3 days, but occasionally a 4 day hike); Usually McDoubles (or any hamburger without mayo) and Beef Burritos (without sour cream) with the occasional deli sandwich. I prefer to mix up my fast food on a trip to avoid getting sick of the same thing. Stopping at a drive thru or two makes it easy to buy your food for a trip while on the road to the trailhead. The amount or preservatives and spices (in the case of burritos) insures they will last several days. Even cold they taste better than most backpacking food. But for longer trips or stretches between resupply, I may carry out something for the 1st day, but the rest of my food is more typical backpacking food.

There is no way I'd want to hike for several months eating the same thing all the time. As an American, it would likely take longer to get sick of a cheeseburger than other things, but there is more to eating than just calories. Long term, I have to question the lack of nutrition which effects how well your body can utilize those calories and the lack of fiber on your GI.

When I saw that PCT Youtube video of the Mcdouble challenge years ago, I could relate somewhat to what he did given I've often carry the same thing on hikes, though with slightly more variety. His follow up video eating nothing but McNuggets on another section didn't even sound good to me and sure enough didn't work out so well.